Surface treated rubber articles



United States Patent O SURFACE TREATED RUBBER ARTICLES lawrence Michael Dadson, Manchester, England, assignor to Imperial Chemical Industries Limited, London, Engv land, a corporation of Great Britain No Drawing. Application October 21, 1957 Serial No. 691,159 1 Claims priority, application Great Britain I 7 October 22, 1956 6 Claims. or. 117-139) ture. In particular, the electrical insulation properties of a latex rubber vulcanisate rapidly deteriorate when the vulcanisate is kept in a moist atmosphere. As a result of this, latex rubber has not hitherto been considered to be of value for electrical applications, for example in electric cables.

It has now been found that this deterioration can be minimised by the treatment of the rubber, before vulcanisation, with certain complex derivatives of chromium. These complex derivatives of chromium are described in US. specifications 2,273,040, 2,356,161 and 2,524,803, being complex chromium compounds of the Werner type in which a trivalent nuclear chromium atom is coordinated with a carboxylic acido group, for example stearato, oleato or laurato chromic chloride or nitrate.

Thus according to the present invention there is provided a process for improving the resistance of rubber compositions to the vaction of moisture which comprises treating the surface of the rubber composition, before vulcanisation, with a complex chromium compound as hereinbefore defined.

The rubber compositions may be made from natural or synthetic rubbers, for example polymers and copolymers of butadiene, including copolymers with for example styrene or acrylonitrile, or mixtures thereof. There may also be used grafted natural rubbers, that is to say rubbers which are made by polymerising a suitable monomer in rubber latex so as to form side chains on the rubber molecule, for example a natural rubber/styrene graft polymer.

Pigments, fillers, antioxidants, stabilisers, accelerators, and other known adjuvants of value in the manufacture of rubber compositions may also be incorporated in the rubber compositions by known procedures.

The process of the present invention is effective in improving the properties, particularly the electrical properties, of rubber compositions, especially those compositions made from a latex rubber. The rubber composition is made in known manner, incorporating any desired adjuvants, and is formed into the desired shape, for example by dipping or slush moulding. It is dried, and is thereafter treated with the complex chromium compound, and then vulcanised in the usual manner, for example by heating in hot air. p

The complex chromium compound of the Werner type may contain a trivalent nuclear chromium atom coordinated with any carboxylic acido group, for example acido groups derived from fatty acids, for example stearic acid, lauric acid, and oleic acid, or unsaturated acids for example methacrylic acid and isopropyl acrylic acid. The chromium atom may also be coordinated with other 'ice 2 molecules, atoms or radicals, for example water or chlomm.

The complex chromium compounds are conveniently manufactured according to the processes described in the above U.S. specifications, as water-soluble solids or as solutions in lower aliphatic alcohols, for example isopropanol. Thus they may be made by heating a basic chromium salt, conveniently a basic-chromium chloride, with a carboxylic acid substantially in the absence of water, or by reducing chromium trioxide or chromyl chloride to a salt of trivalent chromium while in contact with a carboxylic acid, for example by reduction with an alcohol.

The complex chromium compound may readily be applied to the rubber composition for example from solution by dipping techniques.

The quantity of the complex chromium compound to be applied in the process of the present invention is not critical, and a suitable quantity may conveniently be applied by dipping the rubber compositions in solutions containing approximately 2% of the complex chromium compound. v

The invention is illustrated but not limited by the following examples in which the parts and percentages are by weight. l

Example 1 A mix having the following composition, in parts by dry weight, was prepared from a natural rubber latex.

. Latex rubber films were prepared from this mix by flowing the mix on to glass plates and drying at room 1 temperature. One film was vulcanised by heating in air a After 7 days over satu- Freshly prepared rated ammonium chloride solution Untreated film 2.58X10 ohms/cm 0.007X10 ohms cm.- Film treated with 36.3)(10 ohm /cm. 75. 8X10 ohms cm.

methacrylate chromic chloride Example 2 A having the following composition, in parts by weight, was prepared from a natural rubber/styrene graft polymer:

Rubber hydrocarbon r Ethylene oxide fatty alcohol condensate (stabiliser) 0.2 Sulphur 1.0 Zinc oxide 1.5 Zinc diethyldithiocarbamate 1.0

Latex rubber films were prepared from this mix by flowing the mix on to glass plates and drying at room temperature. One film was vulcanised by heating in air at C. for 2 minutes; a second film was steeped for lofiqdndsjn 2.341% solution of stearato chromic chloride in a mixture of isopropanol and Water, and then dried at room temperature, and finally vulcaniscd by Mtiuginair at 150"-..C..-;f or Zrninutes.

The films were allowed to cool at room temperature, and then ttheir .volume electrical resistivity was measured. fl'helfilmsrwere thensuspendedior 7 days in the vapour aboves-ar saturated aqueous solution of ammonium chloride, and then removedand the measurements repeated. Ilhe following values of ,volumeelecirical resistivity were obtained.

Alter 7 days over satu- Freshly prepared rated ammonium chloride solution Untreated film 3.12Xl0 ohms/cm. 0.3)(10 14 ohms/cm. :Film treated with 1.85.2410 ohms/0mm- 9.24X10 H ohms/cm.

. stearatoichromic chloride.

The natural -rubber/stryene graft polymer latex -was prepared by stirring styrene monomer into latex containing tertiary butyl hydroperoxidc and adding tetraethylene pentamine.

What "I claimis:

1. Process for improving the resistance of rubber compositions-to the action of moisture whichcomprises treating the surfaceof the rubber composition, before vulcanisation, with a complex chromium compound of the 'Werner type in which a trivalent nuclearchromium atom is co-ordinatedwith a;carboxylic acido group.

2. Process for improving the resistance of rubber compositions to moisture, as claimed in claim 1, wherein the rubber composition is made from a latex rubber.

3. An unvulcanized rubber composition surface: treated with a complex chromium compound of the Werner type wherein a-trivalent'nuclear chromium atom is coordimated with a carboxylic acidogroup.

4. A vulcanized moisture resistant rubber composition surface treated prior to vulcanisation, with a complex chromium compound of the Werner type wherein a trivalentnuclear chromium atom is co-ordinated with a carboxylic acido group.

5. A rubber composition in accordance with claim 3 wherein the chromium complexis methacrylate chromic chloride.

6. .A rubber composition in accordance with claim 3 whereinthe chromium complex is stearato chromic chloride.

References Cited in the file of this patent UNITED STATES PATENTS .2',273 ,04.0 ,Iler Feb. 17, '1942 2,410,414 Johnson Nov. '5, 1946 2,582,278 "Prentiss Ian. 15, 1952 

1. PROCESS FOR IMPROVING THE RESISTANCE OF RUBBER COMPOSITIONS TO THE ACTION OF MOISTURE WHICH COMPRISES TREATING THE SURFACE OF THE RUBBER COMPOSITION, BEFORE VUNCANISATION, WITH A COMPLEX CHROMIUM COMPOUND OF THE WERNER TYPE IN WHICH A TRIVALENT NUCLEAR CHROMIUM ATOM IS CO-ORDINATED WITH A CARBOXYLIC ACIDO GROUP. 